there is video link
my servo is mige
Keep turning the Allen key until it pops loose.
Sometimes they are really tight.
Hi Sambabaa
Encoders with cone shaft can also be originally tightened to hard, that they simply won’t separate. I’ve made this mistake in the past once, and it was quite a surprise how easily it happened. I hope you don’t have the same issue.
You could try carefully heating/cooling the connection depending on the metals if they have different thermal expansion coefficient.
Kind regards, Esa
I can’t squeeze any more and I’m too scared to push
You could carefully destroy the encoder housing and circuit board that is still mounted to the motor with some channel lock type pliers.
Get to the point that all is left is the brass sleeve.
Then you could grab the brass sleeve with vise grips and get it to brake free.
Or once you are down to just the brass sleeve heat it up a little with heat gun or torch like Esa recommended.
From the video evidence, I would say crank the Allen-key, you’re toying with it 
Use a good quality Allen-key and Allen-cap bolt and let it rip.
Agreed Beano!
I would use a brand new high quality bolt and allen wrench.
If I could not do it with that I would put a hex adapter on a socket wrench.
I have had some grouchy ones over the years, but never one I did not get off. 
Yep, I had an AKM once that was bloody stubborn, but it came off when I got angry enough
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